Imaging Utilized in Diagnosis of CRPC

Transcript: Judd Moul, MD: To play devil’s advocate, I’m a urologist, and most of these patients with non-metastatic CRPC [castration-resistant prostate cancer] are in the urology practices. One of the first questions that I hear is how to identify these patients. Tanya, in your institution, have you figured out a foolproof way to identify these patients? That’s one of the key questions that urologists want to know: how do I identify these patients?

Tanya Dorff, MD: I think it boils down to how often we see these patients and how often we image them. Because we used to not have treatments in this space, it didn’t make a lot of sense to be imaging them very frequently. Now, we really need to know how to categorize a patient who’s been on ADT [androgen deprivation therapy]and whose PSA [prostate-specific antigen] is rising, because we have very different choices, depending on whether the imaging shows metastatic disease. I used to think these patients didn’t exist, and unfortunately, much of the time when you do regular scans, you will find metastasis in a fair proportion. However, I have found a number of these patients by watching them a bit more closely and talking to them about the fact that we now have medications that will delay the time until their scan will turn positive. As Alicia was mentioning, that’s a very new conversation for us to have.

Alicia Morgans, MD, MPH: One thing that is really important to emphasize, which I failed to say but Tanya has alluded to, is that these were standard scans. One of the most exciting things about what we do is that we’re having access to some of these new molecular imaging techniques.

It would be great to hear your thoughts on that. In the PROSPER, SPARTAN, and ARAMIS studies, patients were defined by standard CT [computed tomography] of the abdomen and pelvis, and then by bone scan.

Neeraj Agarwal, MD: Yes.

Judd Moul, MD: Neeraj, let’s get your input on this topic.

Neeraj Agarwal, MD: My take on this is that I agree with you, Judd. This is predominantly a urology-based entity. Historically, we have not started androgen deprivation therapy for patients who do not have metastatic disease. My approach to these patients, in the absence of any valid treatment options, used to be to delay androgen deprivation therapy for biochemical recurrent disease. The numbers of M0 [nonmetastatic] CRPC are going to go down because of these newer emerging scans—the fluciclovine PET [positron emission tomography] scan or PSMA [prostate-specific membrane antigen]-based PET scans. They are going to pick up metastatic disease.

The first question is, are we really treating M0 CRPC or M1 [distant metastasis] CRPC? From the patient’s perspective, it doesn’t really matter. If PSA doubling time is low and they have metastatic disease—1 bone spot on a PSMA or fluciclovine PET scan, or no bone lesions on a traditional bone scan—I know he is going to develop metastatic disease very soon, so it’s great to have treatment options for these patients.

Judd Moul, MD: You make a great point that from a patient perspective, they don’t want to have metastasis. Maybe I’m thinking too simplistically, but now we have 2 fairly straightforward oral options that either urologists or medical oncologists should be very comfortable in giving. Why open up a Pandora’s Box of metastasis? Why do this sophisticated imaging when you can do standard imaging, and reassure the patient, “Sir, you don’t have any metastasis. We’re going to start you on this very well-tolerated oral medication, and it is likely to give you at least 2 years without having metastasis.” Am I thinking too simplistically as a urologist? Some people say, “I want to do the PET scan. I want to do that PET scan so I can find some spots to radiate. I want to find that oligometastatic disease so we can zap those spots.” Do any of the panelists want to make a further comment on the imaging? Tanya, what do you think? Should we be doing this fancy imaging, or should we keep it simple?

Tanya Dorff, MD: As medical oncologists, we’re information junkies. Having the information about where the disease is does open up some options, but it is important to remember that all the trials in M0 CRPC, and largely in metastatic CRPC, have used conventional imaging to define patient populations. Later on, when we talk about the high volume, that’s all conventional imaging. We don’t actually know whether there is disease there when we do a Gallium PSMA scan and find a spot. We still don’t have large bodies of data with histologic verification that what the PET scan sees is cancer, and we don’t know whether that person is living longer when we radiate it. There are a lot of trials that are beginning to collect data on that, and I would much rather my patients get advanced imaging on a trial where we will learn both the accuracy and the impact of having done that. However, if you’re simply looking for disease to radiate, the advanced imaging is more likely to find it.

Transcript Edited for Clarity